1. Field of the Invention
The invention relates to a valve actuator operated via fluid pressure. The invention allows convenient location of ports for supplying pressurized fluid to various sections of the actuator such that two pistons and two racks cooperatively rotate a member used to mechanically actuate a valve. As the supply ports are more conveniently located on the valve actuator, position sensors and pilot valves may themselves be located closer together, thus permitting integration of the position sensors and pilot valves.
2. Description of Related Art
Conventional actuators used for operating valves may use electric motors, electric solenoids, gas pressure or hydraulic pressure to provide a mechanical input to actuate the valve. In the field of fluid pressure operated automatic valves, diaphragms and rotary actuators use pressurized fluid to cause a valve to change state between open and closed positions.
Conventional rotary actuators use either linkages or a rack and pinion arrangement in order to rotate a shaft or other rotatable member. The rotatable member is connected to a different shaft or stem on a valve, typically a ball-valve or butterfly valve. When the rotatable member rotates, the stem on the valve also rotates causing a ball or butterfly inside the valve to move from a fluid-blocking position to a fluid-passing position, or vice versa.
Whether using a linkage arrangement or a rack and pinion configuration, fluid powered actuators use an air cylinder with a piston. The piston moves in response to high or low fluid pressure supplied on either side of the piston.
Some conventional actuators use two air cylinders. In these designs, a piston in one cylinder moves in the opposite direction of the piston in the other cylinder. Thus, the pistons move inward or outward together. The cylinders are offset and, in unison, push or pull racks that rotate a central pinion. In order to simultaneously apply pressure to the outer ends of each cylinder, a tee is plumbed in line with the pressurized fluid supply. The tee connection splits supplied pressurized fluid into two separate streams, one for each of the two cylinders.
In some conventional actuators, a tee is built into the actuator itself as an integral part of the actuator housing. FIGS. 1a and 1b are top views of one such arrangement including a conventional rotary actuator 1 with left and right pistons 5 and 7 enclosed in housing 3. As shown in FIG. 1a, compressed air travels into port 19, located on a lateral side of the housing. The compressed air from port 19 moves pistons 5 and 7 and their corresponding attached racks 13 and 15 apart, thus rotating the rotary member 18 and pinion 17 in a counterclockwise direction. While compressed air enters volume 10 through port 19, air from volume 11 on the right of the piston 7 and the volume 9 on the left of piston 5 flows out port 21, also located on a lateral side of the housing. To make the actuator reverse direction, compressed air is supplied to port 21, and port 19 acts as a vent as shown in FIG. 1b. Thus, by providing an integral tee 23 connecting volumes 9 and 11, no external plumbing to create the tee is needed.
However, as the integral tee 23 requires space within the housing 3, the housing 3 must be made large enough to accommodate the fluid passages that split the pressurized fluid supply and connect each of the cylinders. As actuator housings also require many other types of connections/mounting holes or other features to be built into the housing, especially on the top of the housing, conventional valve actuators must compromise between placement of the integral tee and placement of the other connections/mounting holes required to operate the actuator. The passages forming the integral tees are typically drilled into the housing. Therefore, to reduce complexity of the manufacturing process, the passages integral to the housing are made with as few bends as possible, and placement of the tee internal to the housing without interference with other connections/mounting holes becomes more difficult. Thus, the ports 19 and 21 and their corresponding passages are typically located on a lateral side of the housing.
Position sensors are typically used to monitor the position of the rotary member in the actuator. The preferred location for mounting the position sensors is a surface of the actuator 1 in which the rotary member 18 is mounted. As one end of the rotary member 18 is configured to connect to a stem or shaft from the valve, the surface of the actuator 1 opposite the valve remains available to mount the position sensors. In most orientations of the actuator 1 and valve, this preferred surface is on the top of the actuator, but as the actuator 1 and valve may be differently oriented than as shown in FIGS. 1a and 1b, the surface opposite the valve may not be on “top” of the actuator. The valve position sensors occupy some of the available area on the housing. Thus, in conventional actuators, the ports 19 and 21 must be located on a different side of the actuator than the one on which the valve position sensors are located.
To supply pressurized air or to vent the ports 19 and 21 as needed, pilot valves are often used. The pilot valve is often an electric valve that responds to a signal sent from a computer control such as a programmable logic controller (PLC). For best performance and convenience, the pilot valves may be mounted directly on the actuator 1 near the ports 19 and 21.
To save space, decrease manufacturing cost, and increase convenience to the user, a need exists to integrate the position sensors and the pilot valves used to operate the actuator. However, because of the above-noted space constraints, it has been difficult to locate the pilot valves and position sensors on the same side of the housing. Therefore, integration of the position sensors with the pilot valves has been difficult. Accordingly, a need exists to simplify the way in which pressurized fluid is supplied to the ends of the actuator cylinders so that manufacturers are free to position fluid supply ports on the housing with fewer hindrances. Additionally, a need exists to allow placement of an integrated position sensor/pilot valve combination on the side actuator that is opposite the side at which the valve is attached.